Oil Management System

ABSTRACT

Method and a system for oil management where a common pressure shield contains all oil management functions for treatment of the mixture of oil and refrigerant leaving the compressor, and returning the oil to the compressor. The pressure shield may comprise at least the following components related to oil management; an oil separator from which oil is flowing to an oil sump, an oil cooler connected to the oil sump, a mixing valve in which the oil from the oil cooler is mixed with oil from the oil sump for achieving an optimised oil temperature, an oil filter for filtering the mixed oil, the mixed oil being returned from the oil filter to the compressor, and where at least the mentioned components can operate at a pressure level substantially equivalent to the discharge pressure at the compressor.

FIELD OF THE INVENTION

The present invention relates to a method and a system for oilmanagement primary related to a refrigeration system, where compressionmeans has an discharge for refrigerant connected to means for oilseparation, from which oil separation means, oil is led back towards thecompression means.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 5,347,821 describes a method and apparatus for monitoringoil charge loss for use with a refrigeration system. The refrigerationsystem has a compressor for compressing a refrigerant gas, an oil/gasseparator for separating compressed refrigerant from lubricating oil, acondenser for condensing the compressed refrigerant gas, an oil coolerfor cooling oil separated from the refrigerant, the refrigerant and oilboth having known and differing coefficients of heat transfer, and aninjection system for injecting the cooled oil into the compressor.

WO 03/027586 A1 concerns a liquid purger for purging liquid from a gaswhere the liquid purger has a constantly open passage for flow of gasand purged liquid, the passage being connected to a return duct wherethe flow is controllable, and where the return duct can lead gas and thepurged liquid back to e.g. a cooling compressor or to a reservoir in theclosed circuit. The invention is based on the view that by establishinga weak fluid flow from the bottom of a pressurised vessel in whichpurged liquid may occur, it is possible to lead this liquid flow througha narrow passage in a pressure loaded valve piston in such a way thatthis through-flow may occur without any visible influence on theposition of the valve piston as long as there is only gas, whereas anincreased pressure is built up against the valve piston upon theappearance of liquid in the flow due to the higher density and viscosityof the liquid, whereby the piston is pushed back against the pressureload and thereby opens a wide return duct for the supplied fluid so thatit is returned to its area of application.

EP1434022A2 describes a heat exchanger comprising an elongated housing,a group of parallel pipes placed in the housing for passing a coolingmedium there through, on which pipes a series of cooling plates havebeen arranged for cooling a medium to be cooled in the housing, whereinthe housing has a round cross-section, wherein the cooling plates intheir plane have a geometry composed of several plate portions,particularly plate portions having a separately distinguishablegeometry. Preferably the cooling plates have a geometry composed ofseveral rectangular plate portions originating from the same web ofmaterial and placed adjacently to each other.

OBJECT OF THE INVENTION

The object of the invention is to provide method and a system for oilmanagement where a common pressure shield contains all oil managementfunctions for treatment of the mixture of oil and refrigerant thatleaves the compressor, and returning the oil to the compressor. Afurther object of the invention is to perform efficient liquidseparation and return the oil in the optimum cleaning and temperaturecondition.

DESCRIPTION OF THE INVENTION

This can be achieved in a system where the compressor discharge canoperate in conjunction with at least one pressure shield, which pressureshield may comprise at least the following components related to oilmanagement: an oil separator from which oil is flowing to an oil sump;an oil cooler connected to the oil sump, a mixing valve in which the oilfrom the oil cooler is mixed with oil from the oil sump for achieving anoptimised oil temperature, an oil filter for filtering the mixed oil,the oil being returned from the oil filter to the compressor, and whereat least the mentioned components can operate at a pressure levelsubstantially equivalent to the discharge pressure at the compressor.

It is hereby achieved that all the oil components can operate in anenvironment having a high pressure level so that the shielding of thecomponents only needs very limited material strength because there is noor only a small pressure difference to overcome. Also from an energypoint of view, it is very efficient to keep the oil at more or less thesame pressure level so that the oil that is returned to the compressorhas a sufficiently high pressure level related to the oil inlet of thecompressor. The combination of the oil components inside the pressureshield reduces the number of pipes that otherwise would be necessary foroil management around a refrigeration system. The reduction of highpressure pipes also reduces the risk of leaks in any of the tubing wherea leak could lead to a loss of oil but also to a loss of refrigerant.

The compressor discharge is connected directly to the inside of thepressure shield the bottom of which forms the oil sump. The oil ispressed through oil separators before the refrigerant leaves thepressure shield through a piping. The oil that has been separated fromthe refrigerant is flowing downwards to the oil sump.

The oil cooler is preferably formed as a longitudinal heat exchangerthat can be placed angled at a first angle related to the longitudinalaxis of the pressure shield. It can hereby be achieved that the lengthof the heat exchanger can increase to a length higher than the length ofthe shielding. It is also possible that one end of the heat exchangerhas its inlet submerged in the oil sump, where the upper part of theheat exchanger is placed in the upper part of the pressure shield.

The first angle of the heat exchanger related to the longitudinal axisof the pressure shield might be at least 8 degrees. It is herebyachieved that the heat exchanger can form a thermo siphon.

It is preferred that the heat exchanger comprises a number oflongitudinal pipes surrounded by fins, where a refrigerant can flowinside the pipes, where oil can flow outside the pipes, and where heatcan be transmitted from the oil towards the refrigerant. It can herebybe achieved that an extremely big surface can be used for thetransportation of heat from the oil towards the refrigerant.

The heat exchanger can be formed inside a heat exchanger shield, whichshield can have inlet openings in the lower part for forming an accessto an oil sump formed in the lower part of the pressure shield. In thisway, it is achieved that the oil has access to the oil sump and willfill up at least the lower part of the heat exchanger. Because of therelatively high pressure inside the pressure shield, this pressure willpress the oil upwards through the heat exchanger, if from the top of theheat exchanger, there is one or another connection towards a lowerpressure level.

Longitudinal channels can be formed inside the heat exchanger shieldbetween the shield and the fins of the heat exchanger. The channelsinside the heat exchanger shield are necessary for having a flow in anupwards direction inside the shield simply because the fins of the heatexchanger otherwise would block for the flow in the upwards direction.By generating these channels, there can be a flow upwards and dependingon how the inlet and the discharge are placed in the heat exchanger, itis possible that all the oil has to pass through the heat exchanger atleast once in a direction along the fins and perpendicular to the heatexchanger itself.

Channels between the heat exchanger and the related shield can be partlyblocked for forming at least two sections, where oil is forced to flowbetween the fins for flowing from a first section to a second section.By blocking one of the channels so that only one channel is open, theoil can be forced to pass along the fins perpendicular to the directionof the heat exchanger several times depending on the number of blockingelements that are placed along the heat exchanger. A change in directiontwo to four times along the heat exchanger is probably preferred.

The heat exchanger can be formed with a separated section, where theheat exchanger shield has an inlet and an outlet for a cooling medium,which can be used for cooling electronic switches, which control a motorconnected to the compressor. This can lead to a reduction of thephysical size of the electronic equipment that might be used for drivingan electric motor, which drives a compressor. By using liquid cooling ofthe power electronic components, for example IGBTs or othersemiconductor switches, an effective cooling can take place which has arelatively small volume compared to what should have been the case ifair cooling was used. The amount of heat that has to be removed from theelectronic circuit could be as high as a few percent of the totalelectric power that is used for driving the compressor. Therefore, thecooling demand for the electronic circuit could be several kilowatts.

The invention can also be expressed as a method for oil managementprimarily related to a refrigeration system, where compression means hasa discharge for refrigerant connected to means for oil separation, fromwhich oil separation means, oil is lead back towards the compressionmeans where the compression means is operating in conjunction with atleast one pressure shield, which pressure shield comprises at least thefollowing operations related to oil management, separating oil fromrefrigerant, cooling the oil, filtering the oil, and returning oil tothe compression means, which operations are performed at a pressurelevel substantially equivalent to the discharge pressure at thecompression means.

By this method, oil can be managed at the pressure, which it has when itleaves for example a compressor. In this way, all the differentcomponents for oil management are placed inside the same shield whichmeans that the casing of the different components do not need toovercome the high pressure. The level of the pressure leaving thecompressor depends on the refrigerant, which is used.

The oil can be cooled in a longitudinal heat exchanger placed angled ata first angle related to the longitudinal axis of the pressure shield.This is only one possible way of forming the heat exchanger. Other heatexchangers having a very effective heat transmission between the oil anda cooling medium could be used. The longitudinal heat exchanger has theadvantage that at least from one end, it could be possible to get accessfor refrigerant to the heat exchanger, and probably from the same endboth inlet and a discharge can be placed side by side. In this way,refrigerant from the suction side of a refrigeration system could beused in the oil cooler. This refrigerant could come directly from anevaporator where an increasing temperature of this refrigerant onlylimits the risk of sending liquid refrigerant towards the compressorinlet. Especially if the compressor is a piston compressor, liquidrefrigerant in the suction side of the compressor would destroy thecompressor because liquid refrigerant cannot be compressed.

Preferably, the heat exchanger may comprise a number of longitudinalpipes surrounded by fins, where a refrigerant can flow inside the pipes,where oil can flow outside the pipes, where heat can be transmitted fromthe oil towards the refrigerant. By letting the refrigerant flow insidethe pipes, an effective cooling occurs by the fins, which have a verybig surface that is in contact with the oil. The oil flow between thefins could be very turbulent which also will increase the heattransmission from the oil towards the refrigerant.

The oil might flow inside a heat exchanger shield, which shield can beformed with inlet openings in the lower part for forming an access to anoil sump formed in the lower part of the pressure shield. Forming ashield around the heat exchanger can lead to only a certain amount ofoil being cooled down by the refrigerant so that only a small amount ofoil can continuously be delivered back to the compressor at a lowtemperature. The great amount of oil that fills up the oil sump can havean increasing temperature without damaging the surroundings, and onlythe small amount that is used for the compressor is treated by the oilmanagement system as such.

The oil can flow in longitudinal channels inside the heat exchangershield between the shield and the fins of the heat exchanger. Thelongitudinal channels simply increase the oil flow inside the shieldbecause the fins of the heat exchanger are partly blocking the flow inthe longitudinal direction of the heat exchanger.

The oil can flow in the channels, which between heat exchanger and therelated shield are partly blocked for forming at least two sections,where oil can be forced to flow between the fins to flow from a firstsection to a second section. By separating the heat exchanger intosections, the oil is forced to circulate along the fins perpendicular tothe direction of the heat exchanger. This will increase the heattransmission between the oil and the refrigerant.

The heat exchanger can be formed with a separated section for cooling amedium used for cooling electronic switches, which controls a motorconnected to the compressor. It can hereby be achieved that the samerefrigerant continues in elongated channels into the extra section ofthe heat exchanger, but where this heat exchanger is cooling a medium,which is used for cooling the electronic circuit. This will lead to avery effective electronic cooling, and big air blowing equipment is notnecessary for cooling the power electronic components.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a refrigeration system according to the invention,

FIG. 2 shows a sectional view of a pressure shield comprising an oilcooler formed as a longitudinal heat exchanger,

FIG. 3 shows a sectional view according to the line A-A in FIG. 2,

FIGS. 4 and 5 show a sectional view according to the lines D-D,

FIG. 6 shows a sectional view according to the lines C-C, and

FIG. 7 shows a refrigeration system using refrigerant for oil-cooling.

FIG. 8 shows the same refrigeration system as FIG. 1 but modified foruse of refrigerant for oil cooling.

FIG. 1 shows a refrigeration system 2 which system comprises an oilmanagement system 4. The system 2 also comprises a motor 5 that drives acompressor 6 which compressor 6 is connected to a suction line 8 whichline 8 is connected to valve means 7. The compressor 6 has a discharge10, which is led into a pressure shield 14. Inside the pressure shield14, oil-separating means 12 is placed which means 12 comprises a firstdemister 26 which is built up of a number of travel plates. Therefrigerant hereafter passes through an angled demister 28 for furtheroil separation. A line 30 leads to a fine separator 32 that is able toseparate even small particles of oil. Refrigerant leaves the fineseparator 32 through a line 34 which is connected to an outlet valve 35.The fine separator 32 has an oil outlet 36 which is connected over aline 37 to an oil return valve 46. From this oil return valve 46, a line48 leads the oil back to the compressor 6. The pressure shield 14comprises an oil sump 42. Submerged in this oil sump, oil cooler 22 isplaced. This oil cooler has an oil suction line 50 in the oil sump 42from where oil 16 is sucked through a first raw filter 52 before the oilreaches the oil cooler 22 which might be a heat exchanger where the warmoil is heat exchanged by a medium that is led into the oil cooler 22from an inlet 38, and where this medium leaves the oil cooler through anoutlet 40. The cooled oil leaves the oil cooler 22 through a line 54which leads to a mixing valve 56. This mixing valve 56 has an oil inlet58 also connected to the oil sump 42. An outlet 60 from the valve 56contains oil at the optimised temperature, and this oil is led throughthe line 60 to a service valve 62. From there, the oil is led to the oilfilter 24. The oil filter 24 is connected to a service valve 24 forevacuating the oil filter 24. The oil filter 24 has an outlet 63 whichis led to a further service valve 66. From this service valve 66, a line68 leads to the compressor 6.

During operation, warn refrigerant mixed with oil 16 is led into thepressure shield 14. The refrigerant is pressed out through oilseparators 12 which contain demister arrangements 26, 28 for catching asmuch as possible of the oil 16, which is contained in the refrigerant 8.This oil 16 drips downwards forming an oil sump 42. This oil 16 hasnearly the same pressure as the discharge pressure of the compressor 6.From the angled demister 28, the refrigerant is sucked out through aline 30 where the refrigerant is further separated from its content ofoil in the next fine demister 32. The oil that is caught in the finedemister 32 is delivered through a line 36 directly to the compressor 6over an oil return valve 46. In the oil cooler 22, oil from the oil sump42 is cooled down and led back over a line 45 to the mixing valve 56where this relatively cool oil in the line 54 is mixed with warm oilfrom the oil sump 42. Depending on the temperature in the oil sump, themixing valve 56 opens or closes the inlet to the line 58 for achievingthe optimal temperature in the line 60. In this way, the oil temperaturethat is led back into the compressor can be kept at a temperature level,which is optimal for the compressor. This optimal temperature can beachieved in nearly all operational situations independently of the loadon the compressor.

In FIG. 2, the oil cooler 122 is formed as a longitudinal heat exchanger130. The heat exchanger is placed angled with the first angle 132 inrelation to the longitudinal axis of the pressure shield 114. The heatexchanger 130 comprises longitudinal pipes 134 surrounded by aperpendicular fins. The heat exchanger is formed inside a shield 138which shield 138 has openings 140 for inlet of oil. Inside the shield138, channels 144 for oil circulation are formed. In the lower part ofthe pressure shield 114, an oil sump 142 is present. The heat exchanger130 has an elongation 150 in which the pipes 134 continue, but whereanother cooling medium is surrounding the pipes in the section 150. Thiscooling medium has an inlet 154 and an outlet 156. In the lower end ofthe heat exchanger 130, the channels 134 are ending in a chamber 158.Into this chamber liquid refrigerant from the condenser or receiver at ahigher geodaetic level is lead and at the other end of the heatexchanger 130, the outlet 161 is connected to the condenser or receiver.The flange 163 is in this configuration blinded. Due to the partlyevaporation that occurs at the heat exchange a self-circulating systemis established; known as a thermosiphon. Another option is to cool theoil by water or brine pumped by force into 163 and returned at 161 withthe cavity 158 acting as a returning chamber. Further, an oil valve 164that is connected to an oil return line 168 is shown. During operationof the invention as shown in FIG. 2 the oil flows through openings 140into channels 144, 146, 148 inside the heat exchanger 130 where pipes134 are cooled by circulating a cooling media. This cooling media can bewater or brine or a refrigerant. In the inlet, a liquid cooling mediamight flow, which media is partly or fully evaporated when leaving theheat exchanger. Between the pipes 134, fins are placed so that the oilhas to circulate between the fins in order to come from one of thechannels 144 to the other channel 146, 148. These channels 144, 146, 148can be placed so that the heat exchanger 130 is separated into sections146,148 by shields 145, 147. The oil 116 is circulating upwards alongthe pipes 134 and changing from the channels 144, 146, 148 maybe up to10 times before the oil reaches an oil outlet, which is connected to anoil filter 124. From this oil filter 124, oil is sent towards a valve 16for mixing the cooled oil with warm oil for achieving a preferredtemperature for the compressor. When this valve 164 opens, there is anoil connection through an oil line 168 into the compressor at a pressurelevel, which is sufficiently lower than the discharge pressure, whichwill suction the oil into the compressor. Further, an inlet 160 forrefrigerant 108 and an outlet 162 for the refrigerant 108 are shown onthe figure.

FIG. 3 shows a sectional view of FIG. 2 according to a line A-A. FIG. 3shows an angled demister 228, which internally has a piping 230 in whichrefrigerant flows out from the demister and towards a fine demister,indicated as 32 in FIG. 1. FIG. 3 further shows an inlet 261 and anoutlet 263 for a cooling medium that flows in the pipes 134 shown inFIG. 2, which are indicated below the inlet 261 and outlet 263. A valve262 is shown which valve is a manual closing valve that can isolate theoil filter 224 from all the other parts of the system, see FIG. 1 valve62. A further valve 266 is placed for closing the outlet of the oilfilter, see FIG. 1 valve 66. A valve 264 is also indicated which valve264 is an oil-mixing valve where cooled oil is mixed with warm oil forachieving the optimized oil temperature for the compressor.

FIG. 4 shows a sectional view of FIG. 3 at the line B-B. FIG. 4 showsthe cut-off valve 262, the cut-off valve 266 and the mixing valve 264.Leading away from the shut-off valve 266, the start of piping 268 isshown which piping is the oil pipe that leads purified andtemperature-regulated oil back to the compressor.

FIG. 5 shows a sectional view of FIG. 2 at the line D-D. FIG. 5 showsthe pipe 238, which comprises pipes 234 for a cooling media. A shield245 is furthermore shown that shields most of the oil flowlongitudinally through the heat exchanger. Only at channel 244 there isan opening where oil can pass from one section of the heat exchanger tothe next.

Furthermore, FIG. 6 shows the pipe 238 and the inner pipes 234 where achannel 246 is open for oil circulation.

FIG. 7 shows the same refrigeration system as FIG. 1 but modified foruse of refrigerant for oil cooling. Only the differences to FIG. 1 aredescribed in the following:

Liquid refrigerant at a high-pressure level is delivered in pipe towardsan expansion valve 70. Expanded refrigerant flows in a pipe 72 to theinlet of the heat exchanger 22. In the heat exchanger 22 the refrigerantevaporates by cooling the oil. Fully or partly evaporated refrigerantleaves the heat exchanger through a pipe 76 which pipe is connected tothe compressor, preferably to a port corresponding to a pressure closeto discharge pressure. The opening degree of the expansion valve iscontrolled by temperature measuring means 74 connected to the pipe 76containing refrigerant leaving the heat exchanger.

FIG. 8 shows the same refrigeration system as FIG. 1 but modified foruse of refrigerant for oil cooling. Only the differences to FIG. 1 aredescribed in the following:

Liquid refrigerant at a high-pressure level is delivered in pipe towardsan expansion valve 70. Expanded refrigerant flows in a pipe 72 to theinlet of the heat exchanger 22. In the heat exchanger 22 the refrigerantevaporates by cooling the oil. Fully or partly evaporated refrigerantleaves the heat exchanger through a pipe 76 which pipe is connected tothe compressor 6, preferably to a port corresponding to pressure closeto discharge. The opening degree of the expansion valve 70 is controlledby temperature measuring means 75 connected to the oil pipe 54 leavingthe heat exchanger 22. This set-up eliminates the need for a mixingvalve 56 (FIGS. 1 and 7).

1. Oil management system primarily related to a refrigeration systemcomprising at least one compressor, which compressor comprises an inletfor refrigerant, which compressor has a discharge for refrigerantconnected to means for oil separation, from which oil separation means,oil is led back towards the compressor characterized in that thecompressor discharge operating in conjunction with a pressure shield,which pressure shield comprises at least the following componentsrelated to oil management; an oil separator from which oil is flowing toan oil sump; an oil cooler is connected to the oil sump; a mixing valvein which the oil from the oil cooler is mixed with oil from the oil sumpfor achieving an optimised oil temperature; an oil filter, for filteringthe mixed oil, where the oil is returned from the oil filter to thecompressor, where at least the mentioned components operate at apressure level substantially equivalent to the discharge pressure at thecompressor.
 2. Oil management system according to claim 1, characterizedin that the oil cooler is formed as a longitudinal heat exchanger angledat a first angle related to the longitudinal axis of the pressureshield.
 3. Oil management system according to claim 2, characterized inthat the first angle of the heat exchanger related to the longitudinalaxis of the pressure shield is at least eight degrees.
 4. Oil managementsystem according to claim 1, characterized in that the heat exchangercomprises a number of longitudinal pipes surrounded by fins, where afirst cooling media is flowing inside the pipes, where oil is flowingoutside the pipes, where heat is transmitted from the oil towards thefirst cooling media.
 5. Oil management system according to claim 1,characterized in that the heat exchanger is formed inside a heatexchanger shield, which shield has inlet openings in the lower part forforming an access to an oil sump formed in the lower part of thepressure shield.
 6. Oil management system according to claim 1characterized in that longitudinal oil channels are formed inside theheat exchanger shield between the shield and the fins of the heatexchanger.
 7. Oil management system according to claim 1, characterizedin that the channels between the heat exchanger and the related shieldare partly blocked to form at least two sections, where oil is forced toflow between the fins to flow from a first section to a second section.8. Oil management system according to claim 1, characterized in that theheat exchanger has a separated section, where the heat exchanger shieldhas an inlet and an outlet for a cooling medium used for coolingelectronic switches, which switches control a motor connected to thecompressor.
 9. Oil management system according to claim 1, characterizedin that the pressure shield has at least one inlet opening forrefrigerant, which inlet opening comprises strainers for a first oilseparation.
 10. A method for oil management primary related to arefrigeration system, where compression means has a discharge forrefrigerant connected to means for oil separation, from which oilseparation means, oil is led back towards the compression meanscharacterized in that the compression means is operating in conjunctionwith a pressure shield, which pressure shield comprises at least thefollowing operations related to oil management, separating oil fromrefrigerant, cooling the oil, mixing the cooled oil with warm oil forachieving the optimal oil temperature in a mixing valve, filtering theoil, and returning oil to the compression means, which operations isperformed at a pressure level substantially equivalent to the dischargepressure at the compression means.
 11. A method for oil managementaccording to claim 10, characterized in that the heat exchanger has aseparated section for cooling a medium used for cooling electronicswitches which switches controls a motor connected to the compressor.